Mansfield Creek (2013)

Background

Twenty-inch wild brown trout from
Mansfield Creek.

In July and August 2013, Region 9 Fisheries staff, along with angler volunteers completed trout population sampling in both the stocked and wild trout sections of Mansfield Creek. Six sites were electrofished, duplicating sites sampled in 1992 and 2008. The stream was also sampled in 2003 where 5 of the 6 sites were the same as in 2013. From 1995-1997, wild rainbow trout were transferred by NYSDEC to Mansfield Creek in order to start a population of these highly catchable trout. In 1992 and 2003, the area where all sites were located was being stocked with hatchery brown trout. However in 2008 and 2013, only the lower two sites were in the stocked section, stocking having been removed where the upper four sites were located in 2004. Sampling in 2013 was done to evaluate the effects of removal of stocking on the wild trout population in this stream and to check for further increases in the introduced wild rainbow trout population.

Electrofishing Results for Wild Trout

In 2013, sampling sites varied in length from 450 to 730 feet and average widths varied from 16-35 feet. For all sampling sites combined, the estimated abundance of adult (yearling and older) wild brown trout was 388/mile, which is much higher than that found in 2008, and near what was found in 1992. Similarly, the abundance of wild rainbow trout in 2013 for all sites combined (327/mile) was higher than 2008 (Table 1). A similar pattern of abundance was apparent when looking at just the sites in the stocked section or only those in the unstocked section (Table 1). However, both species were more abundant in the unstocked than the stocked section in all sampling years. If only sites done in all four sampling years (Sites 2-6) are compared, we see similar abundance for adult wild brown trout in 1992, 2003 and 2013, with much lower abundance in 2008 (Table 1 and Figure 1). For rainbow trout, when comparing Sites 2-6, we see an increasing progression of abundance from 2003-2013 (they had not yet been introduced in 1992) (Table 1 and Figure 1). In the sites located where we no longer stock trout (Sites 3-6), there did not appear to be an increase in the overall abundance of adult wild brown trout since stocking was eliminated in that section, however rainbow trout may have benefited from the removal of stocking, as their population has risen substantially since 2003 (Table 1).

Fish sampling on Mansfield Creek.

Biomass of wild brown trout for all sites combined followed a similar pattern to that seen for abundance, varying from 23 pounds/acre in 1992 to 18 pounds/acre in 2008 and pounds/acre in 2013 (Table 1). In 2013, of the estimated 388 adult wild brown trout per mile, 64/mile were >10 inches, and 45/mile were >12 inches, while 17/mile were >14 inches. The increased abundance of wild rainbow trout from 2003 to 2013 indicates that the population is still continuing to grow, perhaps aided by decreased angler harvest following the elimination of stocking in the upper section of the creek and/or increased voluntary release of trout, similar to what we have seen on other Region 9 streams.

Electrofishing Results for Hatchery Trout

In 2013, at the two sampling sites in the stocked section, a very low abundance of hatchery brown trout were found from the previous spring's stocking. This is similar to 1992, 2003 and 2008 sampling and indicates that water temperatures in that section of stream may not be conducive to survival of the stocked trout through the summer months. It also may be due to poor survival of the hatchery fish even if water temperature is not limiting, as has been witnessed on other Region 9 stocked streams.